1. Field of the Invention
This invention generally relates to four-stroke engines, and more specifically, to a lubrication device that is applicable to four-stroke engines.
2. Description of Related Art
In order to provide common portable work machines, such as lawn mowers, chain saws, and other trimmers with sufficient torque and long-term power, modern industry adopts designs that employ engines of internal combustion as power source. However, the foresaid portable work machines are commonly manipulated at various angles, for instance, a chain saw must be manipulated at various angles in accordance with a specific practical object to be cut, but not maintaining at a same angle; beside, to respond to the demands of manually manipulating light weight and high rotation speed, two-stroke engines are preferable selections of internal combustion engine to four-stroke engines theoretically.
When a foresaid two-stroke engine is operating, it emits exhaust fume and takes in air at the same time; in this situation, the emitted exhaust fume contains some fuel unburned or incompletely burned, such that that using the two-stroke engine will cause exhaust fume pollution, thereby not able to conform to some of the recently issued standards and regulations of pollution emissions. On the contrary, since four-stroke engines have fuel combusted more completely, they conform to the emission standards, Further, four-stroke engines produce less noise than the two-stroke engines during operation therefore it is an inevitable trend to adopt four-stroke engines in the designs of power work machines.
Although four-stroke engines have the advantages of less noise and lower emission pollution, they have disadvantage of requiring proper lubrication on cams and valves of the four-stroke engines, and therefore, a four-stroke engine must be integrated with a lubrication device. However, when a four-stroke engine integrated with a lubrication device is applied to a work machine, such as portable work machines like chain saws, due to the practical application environment, an user is likely to manipulate the four-stroke engine at an extremely slanting or even upside down angle, and at this moment, lubricant stored inside the crank case of the lubrication device is likely to flow into exhaust valves and possibly the flow path of air mixture in the combustion air as well, thereby interfering with effective air combustion and causing engine oil leakage.
In order to overcome the current drawbacks of four-stroke engines applied to portable work machines, some improved designs of lubrication device of four-stroke engines are provided according to U.S. patents, for instance, U.S. Pat. No. 6,213,078, and U.S. Pat. No. 6,170,456, and others.
As shown in FIGS. 1A and 1B, a lubrication device of four-stroke engines is disclosed in U.S. Pat. No. 6,213,078, wherein an oil hole 11 connected to a lubricant tank 12 is disposed underneath a cam room 10, and the lubricant recycles back to the lubricant tank 12 via the oil hole 11. Manipulations of this kind of design at some sloping angles are likely to cause the lubricant to directly reflow to the valve via the cam room 10, and then flow out of the engine via a breathing pipe between valve chamber and air filter.
As shown in FIG. 2, U.S. Pat. No. 6,170,456 discloses a lubrication device of four-stroke engines, which mainly dispose a stirring chamber 14 located on a long and narrow concave underneath the crank case 13, and forms an oil hole 15 at a bottom of the stirring chamber 14 connected to an engine oil tank. Although this kind of design is capable of preventing massive lubricant from flowing into the crank case when the engine is at a slanting angle, it is not capable of providing other mechanical parts of machine, such as cam and gas valves and others, with effective lubrication when the engine is operationally turning over for a long time period. In addition, the traditional breathing pipe that is externally connected to air filter generally is lacks any filtering design, therefore, when the engine is operating at a slanting angle, the lubricant is likely to flow out via the breathing pipe, thereby causing problems of unnecessary lubricant consumption and air filter contamination.
Hence, it is a highly urgent issue in the industry for how to provide a lubrication device of four-stroke engines, which is capable of enabling lubricant to flow into valve chamber and cam room to provide effective lubrication, and meanwhile preventing massive lubricant from flowing into air-intake system to cause engine extinguishment, thereby allowing the user to manipulate engine at various angles.